Currently, various types of package structures have been developed in the semiconductor packaging industry to meet various demands. In a common packaging process, chips are distributed on a substrate, and a packaging encapsulant is then used to encapsulate the chips to complete a package body; meanwhile, solder balls are disposed at the back surface of the substrate for subsequently soldering the package body on a circuit board.
Generally speaking, in a common packaging process, a substrate strip is used to provide a plurality of areas for disposing chips. After all the chips have been distributed on the substrate strip, a packaging encapsulant is disposed on the surface of the substrate strip to encapsulate the chips, and the substrate strip is then divided into a plurality of separate semiconductor package structures.
During a fabrication process, a semiconductor package structure often stays in a high-temperature environment. However, due to the mismatch in coefficient of thermal expansion (CTE) between a substrate and a packaging encapsulant, the substrate and the packaging encapsulant are subject to different degrees of thermal expansion resulting in stress effects, causing a warpage phenomenon; also, because at present electronic products tend to become smaller in size, the overall thickness of the semiconductor package structure decreases accordingly, making the warpage phenomenon in the semiconductor package structure more easily observable.
The variation of warpage of a semiconductor package structure between the room temperature (usually about 25° C.) and the maximum temperature (usually about 260° C.) in a fabrication process usually causes many defects and problems in the products, such as possible poor internal wire bonding in a wire-bonded semiconductor package structure, possible crack of a bump-bonding or a pillar-bonding below a chip of the semiconductor package structure that uses the flip chip technology, or unsatisfactorily attaching solder balls, which are present at the bottom of a semiconductor package structure, onto a circuit board when the semiconductor package structure is disposed on the circuit board.
Therefore, it is necessary to provide a semiconductor package structure and a fabrication method thereof to solve problems that exist in the prior art.